Intradermal injections are used for delivering a variety of medicinal substances into a patient. Many of these substances have proven to be more effectively absorbed into, or react with, the immune response system of the body when injected into the intradermal region of the skin (i.e., when injected intradermally). For example, recent clinical trials have shown hepatitis B vaccines administered intradermally are more imunogenic than if administered intramuscularly. In addition, substances have been injected intradermally for diagnostic testing, such as, for example, using what is known in the art as the “Mantoux test” to determine the immunity status of the clinical subject against tuberculosis and the immediate hypersensitivity status of Type I allergic diseases. It is desirable in some instances to provide a prefilled container such as, by way of non-limiting example, a syringe, filled with a medicinal substance and to also provide a needle cannula that may be coupled to the container just prior to administering the injection.
An intradermal injection is made by delivering the substance into the epidermis and upper layer of the dermis. Below the dermis layer is subcutaneous tissue (also sometimes referred to as the hypodermis layer) and muscle tissue, in that order. There is considerable variation in the skin thickness both between individuals and within the same individual at different sites of the body. Generally, the outer skin layer, or the epidermis, has a thickness between 500–200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5–3.5 mm. Therefore, a needle cannula that penetrates the skin deeper than about 3.0 mm has a potential of passing through the dermis layer of the skin and making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection. Also, the needle cannula may penetrate the skin at too shallow a depth to deliver the substance and result in what is commonly known in the art as “wet injection” because of reflux of the substance from the injection site.
Using a standard needle (i.e., one typically used for subcutaneous or intramuscular injections) to deliver an intradermal injection requires the healthcare professional to perform a complicated and sometime difficult technique; with the success of the injection being dependent upon the experience of the healthcare professional and his/her ability to properly execute the technique. The preferred technique (using a standard needle) requires the healthcare professional to stretch the skin, orient the needle bevel to face upwardly, and insert a 26 Gauge short bevel needle cannula to deliver a volume of 0.5 ml or less of the substance into the skin of the patient. The needle cannula is inserted into the skin at an angle varying from around 10–15 degrees so as to form a blister or wheal in which the substance is deposited or otherwise contained. Accordingly, the technique utilized to perform the standard intradermal injection is difficult and requires the attention of a trained nurse or medical doctor. Inserting the needle to a depth greater than about 3.0 mm typically results in a failed intradermal injection because the substance being expelled through the cannula will be injected into the subcutaneous tissue of the patient.
The most frequent cause of a failed intradermal injection results from inserting the needle into the skin at an angle greater than 15 degrees relative to the flattened skin surface. A further cause of error is derived from pinching rather than stretching the skin in the area of the injection, which is normally done when giving a subcutaneous rather than an intradermal injection (pinching increases the likelihood of giving a subcutaneous injection). Procedural errors as described above result in delivering a medicinal substance into the subcutaneous layer, which can reduce the effectiveness of the injection, as well as possibly delivering the substance in a way not approved for delivery.
Intradermal injections performed by using the technique described above-also are known to cause a significant amount of pain to the patient because of the angle at which the needle cannula is inserted into the skin. By inserting the needle cannula at that angle, about 5 mm to about 6 mm of the needle is actually inserted into the skin. This results in a significant disruption of the pain receptors dispersed throughout the upper layers of the skin. Also, self-administered intradermal injections are not possible using that technique.
Upon completion of an intradermal injection, shielding and disposal of the contaminated needle cannula becomes a primary concern. Because of the great concern that healthcare professionals and other users may become contaminated by accidental sticks from the needle cannula, it is preferable to cover the contaminated needle as soon as the intradermal injection is completed. As discussed in U.S. Pat. No. 5,893,845 to Newby et al., for example, the entire content of which is incorporated herein by reference, developments have been made to provide means for covering the contaminated needle cannula upon completion. These devices usually involve some form of shield arrangement that moves in place over the contaminated needle once it has been removed from the patient. However, these shield arrangements often require the use of two hands to perform the operation of moving the shield over the contaminated needle.
Alternatively, needle cannulas with internal or external blunting cannulas have been used that extend from the needle to blunt the distal end. However, these devices require an operation to drive the blunting cannula into position upon completion of the intradermal injection to protect the user from the sharp end of the needle, yet also must allow use without triggering the safety device. In doing so, such devices can require the internal diameter of the needle to be decreased, which may affect flow of the medicinal substance therethrough, or may require the external diameter of the needle to be enlarged, resulting in unnecessary discomfort to the patient.
Numerous other shielding devices also exist, such as those discussed in U.S. Pat. No. 4,631,057 to Mitchell, for example, the entire content of which is incorporated herein by reference. The device disclosed by Mitchell includes a needle cannula guard which is releasably retained in a retracted position, allowing the syringe to be used for injection, and thereafter, lockably retained in the extended position. A similar device is disclosed in U.S. Pat. No. 4,747,837 to Hauck, the entire content of which is also incorporated herein by reference. Hauck discloses a syringe having a cylindrical sheath sleeve which can be advanced to a locked, irreversible position, which prevents further access to the needle cannula tip. Still other shielded designs, such as the device disclosed in U.S. Pat. No. 4,998,920 to Johnson, U.S. Pat. No. 4,801,295 to Spencer, and U.S. Pat. No. 5,053,018 to Talonn et al., the entire content of each being incorporated herein by reference, allows the needle cannula guard to be moved to an extended position through axial movement without locking the guard. However, in this position, the guard can still be moved to expose the sharp needle cannula tip. These devices also require an additional rotation of the needle guard while the guard is fully extended to place it in a locked position.
Other methods of covering the needle cannula include the use of caps located at the distal end of the syringe. As discussed in U.S. Pat. No. 5,496,288 to Niall Sweeney, the entire content of which is incorporated herein by reference, a protective cap attached at a distal end via a hinged member can be constructed to flip using one finger, from a fully closed position covering the needle, to a fully opened position exposing the needle. This allows a healthcare professional who may be holding a patient or medical instrument with one hand to use the other hand to remove the protective cap, administer a partial dose of medicine, and then conveniently place the cap into a protective position.
Other needle cannula devices have shields that are activated during the procedure when the shield comes in contact with the skin. Using the skin to activate the device is not desirable in all applications however, since the device may not activate if the needle does not penetrate sufficiently, or may cause the shield to inadvertently lock when probing. Such devices may also require excessive penetration into some patients to cause the triggering means to activate the device, which can cause a healthcare professional to unnecessarily change their standard method or procedure.
Of still further concern upon completion of such intradermal injections, and as discussed in U.S. Pat. No. 5,674,203 to Lewandoski, the entire content of which is incorporated herein by reference, is the fact that in many areas in a hospital where such needle cannula devices are used, disposal bins are provided so that a syringe or other needle cannula product can be immediately discarded in a safe, rigid container. However, there are areas of medical practice where disposal containers are not readily available or practical. In these areas, products having some form of permanent shielding device are even more desirable. In these areas, permanent shielding after use allows the device to be safely transported to a disposal system.